These are not lithium, but they are Sealed Lead Acid (SLA) so they won’t leak, and they can be charged with any standard 12V charger. Standard connectors as are found on most ice fishing electronics, so they will work well with no modifications or adapters necessary on most ice fishing electronics.
The deal is Amazon has a set of 6 of the 9Ah batteries for $49 with free shipping. Yes, you get six brand new 9Ah batteries shipped to you for $49.
I have switched to lithium, but that price is fantastic, and you’ll never have to worry about having enough backup power.
Posting links here can be sketchy, so I will just give the item number, and you can search it at Amazon.
Amazon item number B078NJD8SC